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Subject: [SG16-Unicode] NL029 disallow zero-width and control characters
From: JF Bastien (cxx_at_[hidden])
Date: 2019-11-06 03:45:08


SG16 is sending this NB comment to EWG. We'll try to do it between morning
break and lunch.

>From GitHub <https://github.com/cplusplus/nbballot/issues/28>, I expect
that EWG will discuss this for a bit of time:

SG16 in Belfast: Recommend to accept with modification to deprecate
identifiers that do not conform to Unicode TR#31 with exception for use of
underscore.

Rationale: Future direction via D1949R0
<http://wiki.edg.com/pub/Wg21belfast/SG16/D1949R0.html> intends to make
these identifiers ill-formed in C++Future, so we want to put programmers on
notice now to give them time to react. Additionally, we don't want to break
compatibility with C and we lack implementation experience with D1949R0.

We had strong consensus for addressing this concern in C++20. The
recommendation above had slightly better consensus than a poll to, rather
than deprecating identifiers that do not conform to Unicode TR#31, adding a
non-normative note containing guidance that programmers should use
conforming identifiers.

Removing the SG16 label. This now needs to be seen by EWG.

SG16 minutes are available at:

   - http://wiki.edg.com/bin/view/Wg21belfast/SG16NBNL029



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